The present invention relates to a method for the purification of pyrethroid intermediates. More particularly, the present invention relates to a method by which certain byproducts formed during the preparation of pyrethroid intermediates may be removed therefrom.
Pyrethroid intermediates are very important industrial raw materials in that they provide ready access to highly active insecticides. Thus, for example, it is known to react a pyrethroid intermediate, such as permethrin acid ester (PAE) with a cyanohydrin ester, such as metaphenoxybenzaldehyde cyanohydrin acetate to form a potent insecticide, such as NRDC-149 as follows: ##STR2##
It is generally desirable that the pyrethroid intermediate, whether used to prepare insecticides or for other purposes, be relatively free of impurities. Unfortunately, however, the pyrethroid intermediates are often contaminated by the presence of other compounds which are formed as byproducts in the production of the intermediate.
Thus, for example, in Pesticide Science (1974) 5, 791-799 it is shown that the reaction between ethyl diazoacetate and 1,1-dichloro-4-methylpenta-1,3-diene in the presence of copper sulfate to produce ethyl 2,2-dimethyl-3-(2,2-dichlorovinyl)-cyclopropanecarboxylate, results in a product which is contaminated with up to 20% of ethyl fumarate and maleate.
These contaminants are very difficult to remove because they co-distill with the product compound.
In an article by Andre T. Hubert in Synthesis, 1976, p. 600 it is reported that column chromatography or Gas-Liquid chromatography can be employed to separate the desired product from the maleate and fumarate contaminants to produce a pure product.
The use of such techniques, however, is not practical on an industrial scale.
A need therefore exists for an industrially-practical method for purifying the pyrethroid intermediates.